The present application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Patent Application No.2000-315282 filed on Oct. 16, 2000 (12th year of Heisei), the entire contents of which are incorporated herein by reference.
The present invention is generally directed to a soft magnetism metal powder, a method of treating soft magnetism metal powders, a soft magnetism metal formed body, and a method of producing soft magnetism. xe2x80x9cSoft magnetismxe2x80x9d means a property of having a higher magnetic permeability and a reduced residual magnetism by deleting an external magnetic field.
Recently, remarkable advancements have been made in industrial devices or the like requiring soft magnetic materials having higher than usual magnetic permeability. In addition, soft magnetism metal materials are also required to have a higher specific resistance. In order to comply with these requirements, various studies have been carried out in order to provide a variety of soft magnetism metal powders.
For example, prior art references 1 (National technical report, Vol. 40, No. 1, February 1994) and 2 (Japanese Patent Laid-open Patent No. Hei.5 (1993AD)-326289) disclose a technique for providing a soft magnetism material (i.e. a soft magnetism material formed body) with less iron loss, by sintering, at high temperature and under high pressure conditions, soft magnetism metal particles whose surfaces are coated with an oxide. In addition, prior art reference 3 (Japanese Patent Laid-open Patent No. Hei. 5 (1993AD)-47541) discloses a technique for providing a soft magnetism material with less iron loss by sintering, at high temperature and under high pressure conditions, soft magnetism metal particles whose surfaces are coated by mechano-fusion with a soft magnetism material of higher resistive value. However, the above-mentioned soft magnetism metal materials or powders are not always satisfactory when they are put into practical use. Thus, a need exists to provide a soft magnetism metal powder and/or a soft magnetism material formed body which have a much higher magnetic permeability.
In view of the discussion above, the object of the present invention is to provide a soft magnetism metal powder, a method of treating soft magnetism metal, a soft magnetism metal formed body, and a method of producing soft magnetism.
The present inventors have found that a body formed from soft magnetism metal particles has higher magnetic permeability when each of the soft magnetism metal particles, when cross-sectioned, has no more than ten crystal particles. In addition, we have found that the number of crystal particles in each soft magnetism metal particle can be reduced by continually heating the soft magnetism metal particles at a temperature of 750-1350xc2x0 C.
That is, the soft magnetism metal powder of the present invention comprises a majority of particles, each of which has no greater than ten crystal particles on average. This results in a heightened or increased magnetic permeability of the soft magnetism metal powder. By majority, we mean at least 50% of the particles.
The method of treating a soft magnetism metal powder according to the present invention comprises the steps of preparing particles of the soft magnetism metal powder, and heating the particles up to a high temperature in a high temperature atmosphere so that the number of crystal particles in each of the soft magnetism metal powder particles is reduced compared to the number of crystal particles before the heating. This results in a heightened or increased magnetic permeability of the soft magnetism metal powder.
In addition, due to the fact that each of the soft magnetism metal particles has a larger volume than a mass of identical weight and material (i.e., has a relatively low density), heat transfer into each of the particles is rapid, thereby shortening the heating time, i.e., the time required for the crystal particle number reduction process.
The soft magnetism metal formed according to the method of the present invention comprises a majority of soft magnetism metal particles which are coupled together with each other, where each particle of the soft magnetism metal powder has no greater than ten crystal particles on average. The resulting soft magnetism metal powder has heightened or increased magnetic permeability.
The method of producing a soft magnetism formed product according to the present invention comprises the steps of:
preparing a mixture of soft magnetism metal powder; and
pressing, or pressing at a higher temperature the mixture of soft magnetism metal powder, thereby heightening or increasing the magnetic permeability of the soft magnetism metal powder. The soft magnetism metal powder, as described above, has no more than 10 crystal particles in each particle of the soft magnetism metal powder. As will be described below, the soft magnetism metal powder may be coated with a resistance material on its outer surface, such that the resistive material has a higher resistance than the bulk, or parent phase of the particle. The soft magnetism metal powder may also be an alloy of iron, the main component, with an alloying metal which is more readily oxidized than iron, prepared by selectively oxidizing the alloying metal. Such a powder may also have a phosphate acid family conversion treated coating, prepared by applying a treating liquid containing phosphoric acid, or be coated by mechano-fusion. In addition, during the crystal particle number reduction process in which the particles are heated to a high temperature, the number of the crystal particles is reduced (i.e., reducing the hardness of each soft magnetism metal particle), thereby providing a soft magnetism metal formed product having higher density than a soft magnetism metal formed product prepared by press-formation of the soft magnetism metal powder.